You were right to make the thread here. If you made it in recruitment-spam-land you would be invited by derpbillion people who only care about member count.

Here are your questions listed:

1. What should we look for in a guild?
2. What did you, experienced playes, looked for?
3. Were you satisfied with your first election, or did you change several times before finally settling in one?
4. What is the most important thing to have in mind when observing whether to join certain guild or not?

1. Usually people join guilds for one of the following reasons:
   • Social (people to talk to)
   • Community (people to work with)
   • Guidance (ask questions)
   • A title (guild name)
   • To fit in (high member count)
   • "Pro" status (other members are "pro" so you are as well by affiliation apparently)

   You may notice some of these are silly. That is because they are silly.

2. Personally, my first do-want for a guild was people to work with and could rely on; not to lean on and use as a crutch, but if I needed someone to grab something fairly cheap off auction I was unable to afford at the time and could buy from them later or something. It was never about spamming invites to people, begging, or any of that nonsense. It was about respecting each other. After joining the first and only guild I plan to be in for a while, I realized something: guilds are basically just a secondary friends list. If you want to see some ideas to improve guilds see here. I am still in the same old guild which has essentially died (almost no one is active anymore, barely any members; most of them were alternates kicked out) but I stick around because I like the name. Even when the guild was pretty lively it was all about grinding. There were a couple people I had fun chatting with, but when I did a run with them it was all about getting distracted; texting while fighting, getting a snack in the middle of a battlement room, et cetera. It was obnoxious. This happened every time according to another member I asked. No naming. For a new player, though, what you really need is either a guild of helpful people (good luck, there are very few players who would be willing to do this) or a couple veterans to show you the ropes. Be sure to explore different kinds of equipment to find what suits your style best. Do not be pressured into the clone effect. I made a rough guide on equipment here if you have time (hours) to sit down and read before you spend all your hard earned crowns on something you may not like.
3. See above.
4. For the kind of guy who hates conformance and mindless dependence on others, avoid the guilds which spam invites to anyone they see (many guilds do this). At least 80% of the time they are only inviting you to brag how many members they have in their guild, then disband it when no one cares anymore. Also, avoid guilds which have members who beg who are not imminently removed. I have seen guild leaders invite people only to beg for money, energy, and equipment or threaten to remove them. It was hilariously pathetic to watch, and I think I made them cry, but they got what they deserve. Again, no naming. You probably want a guild which has people who are willing to tolerate someone with questions and actively plays. Find those kinds of people. By find I do not mean to stand in the middle of town advertising that you want to give yourself to be at their mercy. Go into the Clockworks, earn your money, get the equipment that suits how you play, and you will very likely run into people who are willing to work with you. Want to know how often you will party with people who like playing with others? In lower tiers, probably pretty often; but when you get around T2 people start to get bitter because of the difficulty change between T1 to T2. Try not to worry about that too much, the change from T2 to T3 is far greater. This is probably very encouraging for you. Be sure to befriend people you enjoy working with. If someone is being a derp (hides in corners during battlement rooms, steals pills/remedies and never needs/uses them, says hateful things to you, etc.) be sure to block them with the ignore feature. If you see them again they will still be blocked in chat.

If you need/want/pretend to want my help add me under the same name I use here. I will probably eventually be able to help you with something. One thing you should know is I like to rock. All the time.

Why, yes, I do write a lot. I wrote this whole post in about three and a half minutes.

Yes, I am also psychic.

Triangle.

...Personally, I'd try to find a friendly guild. Pro status is completely irrelevant to me, although I would be looking to make sure that there are at least members at the same tier (or deeper) as myself, just so that I can at least have some chance of getting help if I need it. I enjoy chatting with my guild, not to mention it's much more convenient than having to use /tell all the time to hold a 3-way conversation.

Don't go for the first guild to send you an invite. Ever. The best thing to do would be to find a guild you like the sound of, then look for an appropriately ranked member and talk to them about the guild first, to get an impression of what they expect from members and what the members themselves are like. One of them I met had a boss run as an entry test to make sure you weren't the kind of person who trolls other players all the time. Others may ask for other things, such as completing a brief questionnaire. Many will require you to be t2 or greater, and some will ask for t3 players only. I would avoid those which ask for donations of CE, cr or high-level equipment as soon as you join (unless they're actively buying it from you, or it's a charity organisation).

Oh, yeah, you probably will want to have a browse through the Guilds section of the forums.

You're welcome to give the guild I'm part of a shot. We're consciously noob-friendly, pretty helpful, fairly active, and we won't take it badly if you jump ship later. :P If you're interested, let me know your in-game name (if different from here) and I'll shoot you an invite.

I doubt anyone would count number of kills. :P
Generally, in that sort of test, people will be looking to see whether you have a good playstyle rather than just pure damage clocked up. The best players are able to adapt to different situations. Some of this depends on having the right gear, but much of it doesn't, and involves compensating for other teammates and taking them into account. One good way of failing this test would be to spam Pulsar line guns and knock enemies around.

I'd consider a good teammate to be someone who takes care when using shieldbumps/weapons with knockback, such as Brandish charges and so forth. Willingness to listen is also excellent; certain bosses such as the Roarmulus Twins require a degree of cooperation in order to be defeated smoothly. My previous guild didn't have a strict limit on the number of CE and non-CE revives necessary, but I suspect anything over 5 per level would be considered excessive. The question is, are you contributing positively to the party as a whole?
If the answer is yes, then I would consider that to be a 'pass'.

You should probably keep in mind that not everyone has this kind of test, though... but generally these are qualities that would be considered desirable in any guild member.