If you venture back in your time machine to the early eighties when I started roleplaying with Tom Moldvay's Basic Set Dungeons & Dragons, levelling up and gaining experience was a varied journey to say the least. Rogues levelled up much faster than the wizard and most of the character classes had different experience targets to gain a level, which resulted in a challenge to balance encounters and how the experience giving affected the in game experience for the players.
Not that we worried about it at the time, it was our first roleplaying game and pre-dated our foray into Marc Miller's Traveller. We simply followed the rules, collecting treasure which equated to experience points when divided between the players; with each character gaining the experience of the treasure they found, with encounter treasure sometimes split equally. The more treasure you found, the more experienced the party became — not something that happens in modern roleplaying games.
I've found that it works for me when all the players receive the same amount of experience every session, that's not to say that every session gives the same amount of experience — they differ, often wildly depending on the action and pace of the scenario — but, that each player receives the same regardless of anything that goes on in play.
I've read many an article advising that rewarding roleplaying with experience points encourages everyone to get involved, along with ideals like keeping in character or playing to your PC's weaknesses should be rewarded with character experience. If this is something that works for you, then great, but for me I don't feel that the approach works. Not everyone will have the same comfort or confidence levels to roleplay 'in character' throughout the session and maybe talking in a funny voice all evening isn't to everyone's taste (making the game experience hugely unenjoyable). It relies on whether as a GM I've given all the players an equal opportunity to excel at roleplaying; have they all had a chance to play out their characters weaknesses; or whether everyone has been able to participate at the same level.
I think this approach puts too much pressure on both the players and game master (which is challenging enough as it is!) to make every session perfectly balanced, which I simply don't think is achievable. I don't think I've ever had a session where every character has had the same opportunities, the scenario will ebb and flow with (hopefully) all players and characters having their moment to shine, but this is not going to be the case in every session of the scenario.
If you do enjoy staying in character and perfecting that gravelly voice that will send shivers down the spine of anyone up to no good — definitely encourage and gently nudge players in that direction. I just don't think experience points are the way to reward, dare I say 'good play', whatever that might be and however you may define it in your gaming group.
My approach is to keep experience simple, with every character gaining the same experience for each session. Now, sometimes the amount of experience may change each session, particularly towards the climax of the adventure — building as the rewards and danger increase, although this will depend on the game system that you're playing.
For those heroic adventurers playing the more recent editions of Dungeons & Dragons, then the default is to share experience equally between the party — despite it's enduring popularity it can be quite difficult to balance experience between encounters, whether they be a non-combat encounter with a street hustler or a full-on dungeon delve. The D20 system is not my personal favourite way of doing things, but maybe I'm in a minority! That said I found the Pathfinder Society, from Paizo, games with their levelling up every three adventures worked quite well for me.
Although if I'm honest, I prefer more skill based games like the goodie but oldie Cyberpunk 2020, the ultimate descent into madness in Call of Cthulhu or the superb background of Legend of the Five Rings (once they went back to their 'normal' system after a foray into D20). These allow for small increases in player ability every session, which is my favourite way of handling experience, and allow PCs to see incremental progress on a session-by-session basis albeit occasionally saving up rewards to increase a higher skill.
This allows everyone, no matter how they participated, and independent of the particular way the scenario unfolded, to see a reward for their endeavours. I would like to think that all your players at the table are there to enjoy themselves, although they may participate in roleplaying games for a variety of reasons and each to their own individual strengths. Rewarding everyone equally will ensure that no play styles dominate, and no one will leave feeling hard done by by having not had an opportunity to fulfil some arbitrary experience point requirement.
Anyway, despite all my waffle, enjoy the way you're playing now, but don't be afraid to experiment to find the best experience point solution for you and your gaming group.